Arrangement for audio frequency amplification



Oct. 15, 1929-. w A F 1,732,031

ARRANGEMENT FOR AUDIO FREQUENCY AMPLIFICATION Filed Sept. 29, 1923 D OUTPUT ELg. i

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LOSE TELEGBAPHIE M. B. 11., OF BERLIN, GERMANY, A CORPORATION 01? (l-EHMAIPTY ARRANGEMENT FOR AUDIO FREQUENCY AMPLIFICATION Application filed September 29, 1923, Serial No. 665,525, and in Germany October 13, 19253.

The present invention relates to an improved arrangement for audio frequency amplification. It comprises vacuum tubes arranged in cascade and has the important ad- 5 vantage that only the first and last transformers of the arrangement are iron core transformers, the vacuum tubes being coupled to each other by high frequency trai'isformers. The amplification can, of course, be increased by using additional vacuum tubes. Regardless of the number of tubes used, however, the arrangement need contain only two iron core transformers, one in the grid circuit of the first tube and the other in the plate or output circuit of the last tube. large number of amplifiers arranged in accordance with the invention can be connected in series without causing howling due to baclncoupling.

1n the drawing,

Fig. 1 is a diagrammatic representation of a circuit arrangement embodying the inven tion; and

Fig. 2 is a diagrammatic representation of a circuit arrangement of modified form also embodying the invention.

In the arrangement represented in Fig. 1 a vacuum tube generator 10 which operates at any high frequency wave is combined with a similar vacuum tube generator 12 which, however, preferably produces a high frequency wave of a frequency different from that of the wave produced by the generator 10. The audio frequency currents to be amplified are impressed upon the grid of the first generator tube 10 by an iron core transformer 14, and the amplified audio frequency may be delivered to a line 16 coupled to the plate circuit of the generator tube 12 by a second iron core transformer 18. In the use of the arrangement, the high frequency generated by the tube 10 is modulated by the audio frequency currents and directed by the radio frequency the tube 12, and the modulated high frequen- Cy 111.

then rectified and detected by means (not shown).

Instead of taking off energy from osciltransformer into the grid circuit of the output circuit of the tube 12 at the end of the cascade arrangement of tubes is any suitable lator tube 12 by means of transformer 18, a

number of amplifying tubes are arranged in the usual manner. Applicant believes that his invention makes possible for the first time the construction of a low frequency amplifier without using any intermediate iron core transformers, and afurther advantage of the invention results from the ability to use high frequency transformers for coupling together the tubes of the arrangement, since the iron core transformers employed in known low frequency amplifiers for coupling the plate circuits of the tubes of the arrz ngement to the grids of succeeding tubes cause very considerable losses in efficiency due to the resistances in the primary and secondary windings of the transformers, as well as hysteresis and eddy currents in the cores of the transformers. Applicant has also found that the elimination of iron core transformers from between the tubes of an arrangement for amplifying audio frequencies causes it to have increased selectivity.

Fig. 2 shows special means for increasing the coefficient of amplification. In the use of the arrangement shown in this figure, not only the grid voltage which is to be amplified, but also a variable plate voltage which supports the amplification is sup plied to the second vacuum tube 12. This aim is achieved by connecting the energy-source of the second vacuum tube 12 in seris with the sccondary winding 2 of a transformer 25, the primary 26 of which is inserted in the direct current plate circuit of the tube 10, whereby the voltage of the current supply circuit of the second vacuum tube 12 is increased or decreased in accordance with the variations of the voltage in the plate circuit of the tube 10. When more than two tubes are included in the arrangement, a transformer secondary 24 can,.of course, be used for each of the tubes following the first one.

Having described my invention, What I claim is:

1. An arrangement for audio frequency amplification comprising a source of audio frequency currents, a plurality of vacuum tube generators of high frequency energy, an

iron core transformer for coupling one of the generators to said source of audio frequency currents, a delivery circuit for the amplified audio frequency currents, and means for coupling the output circuit of the last of said generatorsto said delivery circuit, and radio frequency transformers for coupling the generators together in cascade relation.

2. An arrangement for audio frequency I amplification comprising vacuum tube generators of high frequency energy, said generators being similarly coupled together and one of them operating to produce high frequency energy of a frequency different from that ofthe energy produced by another of the generators, an iron core transformer for impressing audio frequency currents upon the grid circuit of the first of the generators to cause the high frequency energy produced thereby to be modulated in accordance with said low frequencycurrents, and means in the output circuit of the last of the genera tors for delivering the amplified audio frequency currents from the arrangement.

3. An arrangement for audio frequency amplification comprising vacuum tube generators of high frequency energy, each of said generators after the first operating to produce high frequency energy of a frequency different-from that of the energy produced by the preceding generator, an iron core transformer for impressing audio frequency currents upon the grid circuit of the first of the generators to cause the high frequency energy produced thereby to be modulated in accordance with said low frequency currents,

and means in the output circuit of the last of the generators for delivering the amplified audio frequency currents coupling the generators together in cascade relation.

4. An arrangement for audio frequency amplification comprising avacuum tube generator of high frequency current, a second vacuum tube generator of high frequency current having its input circuit coupled with the output circuit of the first generator,

means for coupling-the plate circuit of the second generator to the plate circuit of the first generator and means for impressing the audio frequency currents to be amplified upon the. grid circuit of the first generator.

5. An arrangement for amplifying audio frequency currents comprising a vacuum tube generator of high frequency energy, a second from the arrangement and radio frequency transformers for WALTER SCI-IiiFFER. 

